1. Field of the Invention
This invention relates to cationic methine dyes for paper having excellent affinity for unbleached paper pulp.
2. Description of the Prior Art
Bauman, U.S. Pat. No. 3,742,012, discloses green-yellow pendant cationic dyes for paper having the structure: ##STR3## wherein each of R.sub.1 and R.sub.2 is lower alkyl or cyanoethyl, R.sub.3 is H, methyl, methoxy or chloro, X is -O-alkylene or -NH-alkylene, R.sub.5 is lower alkyl, R.sub.6 is lower alkyl or cyclohexyl, R.sub.7 is lower alkyl or benzyl and A is an anion. The dyes are stated to possess good substantivity on paper.
Buell et al, U.S. Pat. No. 4,017,486, discloses dyes that are structurally similar to the dyes of Bauman and which are stated to have improved storage stability, as compared to dyes of Bauman, in aqueous solutions of acetic acid at temperatures of about 50.degree. C. The dyes of Buell et al are represented by the structure: ##STR4## wherein R is hydrogen or methyl, X is O or NH, n is 2 or 3 and Y is an anion which is halide or methosulfate.
Dyes of even greater substantivity than those of Bauman and Buell et al, however, are desired to alleviate environmental problems relating to the discharge of so-called whitewater from processes for dyeing paper pulp.
According to the present invention, novel cationic .alpha.-cyano-p-(N-benzyl-N-ethylamino) cinnamoyl dyes have been found which have excellent affinity for unbleached paper pulp. The excellent affinity of the dyes permits almost complete utilization of color and results in essentially uncolored whitewater.